A mixed flow fan before the invention of our British Patent No. 1328032 has been understood to comprise a bladed impeller which takes air from an inlet and discharges it with axial and radial components as well as a whirl (or circumferential) component, into a casing which leads the air to an outlet. Some of the kinetic energy of the air leaving the impeller is converted to pressure in the casing.
The invention of our patent 1328082 is a mixed flow fan having an impeller comprising a series of blades supported on a generally frusto-conical central portion, which impeller discharges directly into the ambient atmosphere or a plenum chamber.
The term mixed flow fan as used in the following description is understood to comprise both the fan with direct-discharging impeller of our patent 1328082, and the conventional fan with diffuser casing.